Problem: I cannot do complex OR clauses as I cannot use AND inside OR

[somdoron]

within search OR operation only allow one search key while the protocol allow multiple.
To solve this I added special operator called AND which is allow only within OR clause, the AND just allow unbound array which is inline into the OR operation.

Some examples, if I want to the following IMAP query I cannot do that before this PR:

OR (UNKEWORD DISCARD) (BEFORE 24-AUG-2016 UNSEEN)

trying to do the following yield error:
[['OR', [['UNKEYWORD', 'DISCARD'], [['BEFORE', '24-AUG-2016'], UNSEEN]]]

Now I can do:
[['OR', [['UNKEYWORD', 'DISCARD'], [['AND', ['BEFORE', '24-AUG-2016'], UNSEEN]]]]

which works

If you have another solution for the problem that will be great.